Prone Breast Radiotherapy on the
MR
‐Linac: A Technical Note on Skin‐Couch Contact Dose Effects
Kerryn Brown, Drew Smith, Kristie Matthews, Jessica Lye, Leah McDermott, Michael Chao, Farshad Foroudi, Caroline Wright ABSTRACT
Accelerated partial breast irradiation (APBI) delivers a higher dose to a smaller breast volume with equivalent tumour control to whole breast irradiation and improved cosmesis. The MR‐Linac offers superior soft tissue visualisation and adaptive planning, but limited bore size may result in skin‐couch contact, potentially affecting skin dose. This retrospective pilot study evaluated the effect of MR‐Linac couch contact on skin dose. Three patients with left‐sided breast cancer positioned prone with unavoidable skin‐couch contact were included. MR images were acquired using a 1.5 T MR simulator and contoured for target and organs‐at‐risk. Step‐and‐shoot IMRT plans (30Gy in 5 fractions) were optimised and recalculated with and without magnetic field presence. Dose to the whole skin rind (Skin_Rind) and couch‐contact region (Skin_Rind_Ant) were compared. All plans met target and OAR constraints. Mean Skin_Rind dose was consistently higher with magnetic field presence, while dose to Skin_Rind_Ant was consistently lower. These findings contrast with conventional linac data, suggesting magnetic field and interface effects may alter skin dose deposition.